LB 17-150 - Impacts of upstream forest cover on downstream water quality at drinking water intakes in a developing watershed

Forests are critical in maintaining healthy watersheds. Forest conversion to developed land cover results in decreased water quality and increased flood hazards over time. This conversion further threatens the ability of watersheds to provide stable, clean water supplies at drinking water intakes. Therefore, targeted forest conservation in developing areas could be a strategy for maintaining healthy watershed function, especially near drinking water intakes. However, our understanding of the amount of forest conservation needed to protect water resources remains limited. In this study, we hypothesize that maintaining strategic thresholds of current forest cover relative to predicted future losses will mitigate negative impacts that development has on water quality and quantity. We will test this hypothesis in a rapidly developing US Southeast watershed, which represents a microcosm of development trends happening regionally. We used the Soil and Water Assessment Tool to simulate surface water hydrology in the Middle Chattahoochee watershed, a basin with 60% forest cover. We included 23 municipal drinking water intakes in the model to assess the effects of water quality at these locations. As a pilot study, we tested model sensitivity to land cover by running two extreme scenarios of 1) changing all terrestrial land to forest and 2) changing all terrestrial land to high-intensity development and compared results. Preliminary analyses indicated that flow and sediment were particularly sensitive to the conversion to developed land cover. Complete development increased the flow rate on average by 90% and sediment load on average by 94% at the 23 drinking water intakes, relative to the full forest cover scenario. This sensitivity analysis reveals areas in the watershed that are particularly responsive to land cover change and could be targets for forest conservation. Further scenarios will test the effect that projected land use change by 2070 will have on downstream water quality and quantity, with specific focus on drinking water intakes. This research can further our understanding of the vital role forests play in maintaining healthy watersheds under increasing development.